This invention relates generally to thin film electronic active arrays such as liquid crystal displays or imager arrays and more particularly to static protection devices in displays or imagers having a matrix of electrically conductive transmission lines for controlling active components in such arrays.
Arrays of active electronic devices, such as photodiodes or liquid crystal cells and their associated electrical address lines and switching devices, are typically fabricated on wafers for ease of assembly, testing, and installation in operating equipment. Such arrays typically have one or more layers of electrically conductive components which are electrically insulated from the other. During the fabrication and testing process, static voltages between the layers can rise and fall rapidly as a result of, for example, fabrication process steps (such as metal deposition or reactive ion etching), handling, or application of test voltages.
These static voltages may become large enough to result in the breakdown of dielectric material disposed between the overlying layers of electronic components, destroying or damaging the electronic component at the location where the breakdown occurred. The point at which breakdown occurs is a function of the static voltage, the nature and structure of the dielectric and other materials (such as layers of semiconductor material) disposed between the layers of electrically conductive components, and the surface area of those components. Specifically, breakdown typically occurs at locations in the array which have a relatively small capacitance and are thus less capable of easily withstanding increases in voltage potential between the conductive layers. Differences of potential as low as 50 volts can cause breakdown in some imager arrays. If the number of electronic components damaged or destroyed exceeds the repair capability of the wafer, for example the number of repair lines available to electrically isolate a damaged component (such as is disclosed in U.S. Pat. No. 4,688,896, issued Aug. 25, 1987 to D. E. Castleberry and assigned to the assignee of the present invention), or the operational tolerance for defective devices in the array, the wafer is unusable and must be scrapped.
It is thus an object of this invention to provide an array of electronic components that includes protection from static voltage discharge damage for active components on the array.
It is a further object of this invention to provide an array having static protection capacitors sized such that they exhibit breakdown at static voltages sufficiently low to protect the layers of electrically conductive components forming active components on the wafer.
It is yet a further object of this invention to provide a liquid crystal or photodiode array of enhanced manufacturing yield that is readily fabricated on a wafer and economical to produce.